1. Field of the Invention
The present invention relates to several simple, energy efficient and advantageous processes of producing potassium tetrafluoroaluminate, potassium hexafluoroaluminate and their mixtures.
2. Description of the Related Art
The conventional technical methods of producing potassium tetrafluoroaluminate like (a) reacting alumina trihydrate, hydrofluoric acid and potassium hydroxide, or (b) evaporation of a mixture obtained by combining stoichiometric amounts of the reactive components, or (c) melting together comminuted potassium fluoride and aluminum fluoride at temperatures above 600.degree. C. and grinding the resulting solidified melt, suffer from one or several disadvantages. Some of these disadvantages are product melting at temperatures above 620.degree. C., low yields, or high energy requirements leading to loss of cost effectiveness of the process.
The process described by Willenberg et. al. (U.S. Pat. No. 4,428,920) claims a method for the production of potassium tetrafluoroaluminate melting below 575.degree. C. The process claims the formation and existence of tetrafluoroaluminic acid from a reaction of alumina trihydrate and hydrofluoric acid and forming the tetrafluoroaluminate by subsequent neutralization with potassium hydroxide. The process is claimed to yield a product of melting point not exceeding 575.degree. C. The problem associated with this process is that the existence of tetrafluoroaluminic acid is still debatable in the scientific literature. It is quite likely that the previous art which describes tetrafluoroaluminic acid is a solution of aluminum trifluoride in aqueous HF which may lead to uncertainty of the product composition. Therefore, the prior art becomes limited in scope to produce material of desired composition. It became necessary for us to develop a unique process to manufacture not only the pure forms of Potassium Fluoroaluminates, i.e. KAlF.sub.4 and K.sub.3 AlF.sub.6, but also the products corresponding to different desired mixtures of the two, especially the eutectic composition of the system KF-AlF.sub.3 which melts at 560.degree. C. or below and can be a better candidate as a superior flux (pure KAlF.sub.4 melts at 574.degree. C. and K.sub.3 AlF.sub.6 melts at 985.degree. C.).
Thus, we report here novel methods of manufacturing which are very energy efficient as well as more generally applicable, furthermore, the composition of the end product can easily be tailored to suit the needs by only variation in the ratio of the reactants used.